Potato is highly capital and labour intensive crop. Presently, India is the second largest potato producer in the world. For achieving higher productivity, fertilizer inputs particularly of nitrogen are increasing, which not only enhance the cost of production, but also is a major environmental concern.

Therefore, nutrient efficient varieties which produce higher yields per unit of nutrient applied or absorbed than other varieties under similar agro- ecological conditions play an important role in present day agriculture as the nutrient efficient cultivars would enable farmers to produce at a lower fertility level of the soil.

Central Potato Research Institute, Shimla has developed a number of varieties for different agro-climatic conditions, these varieties vary in their response to nitrogen. It is possible to harvest these cultivars at varying rate of N application. So, yield of potato tuber of different varieties will determine not only N dose but also the extent of their nutrient use efficiency.

Keeping these points in view, an experiment was conducted at Central Potato Research Station, Jalandhar, to find out nitrogen requirement of the popular and new potato varieties and to work out their agronomic use efficiency (AUE) under Indo Gangetic plains of India.

An experiment was conducted for two consecutive years (2009-11) at Central Potato Research Station, Jalandhar. The soil of the experimental field was sandy loam in texture with low organic carbon (0.21%), pH (7.70), available N (245 kg/ ha), available P (30.5 kg/ ha) and available K (297.4 kg/ ha).

Treatments included combinations of eight varieties (Kufri Jyoti, Kufri Jawahar, Kufri Bahar, Kufri Sutlej, Kufri Pukhraj, Kufri Pushkar, Kufri Surya and Kufri Gaurav) and four N levels (0, 80, 160 and 240 kg/ ha), replicated four times in factorial randomized block design. Well sprouted potato seed tubers were planted in the 2nd week of October during both the years.

Half of the N was applied as calcium ammonium nitrate (CAN) in side-band along with a uniform dose of 100 kg P2O5 through single super phosphate and 150 kg/ ha K2O through murate of potash at planting , while the remaining N was applied through urea at 30 days after planting i.e. at the time of earthing up.

Recommended package of practices were followed for raising the crop, haulms were cut at 85 days and harvesting was done 15 days later.

Table 1. Effect of different levels of nitrogen on total tuber (t/ ha) (Pooled over two year).

Varieties

N levels (kg/ ha)

0

80

160

240

Mean

Kufri Jyoti

23.6

30.0

33.2

36.4

30.8

Kufri Jawahar

24.7

32.4

35.3

38.9

32.8

Kufri Bahar

24.6

31.5

35.1

39.6

32.7

Kufri Sutlej

24.6

30.2

35.3

37.8

32.0

Kufri Pukhraj

25.6

33.2

38.3

41.0

34.5

Kufri Pushkar

28.6

39.4

47.4

51.5

41.7

Kufri Gaurav

30.9

42.5

48.1

55.1

44.1

Kufri Surya

20.3

26.7

31.0

34.1

28.0

Mean

25.4

33.2

38.0

41.8

34.6

CD (0.05)

Varieties

1.4

N levels

1.0

VXN

2.8

Kufri Gaurav produced the highest tuber yield at all the levels of N as compared to other varieties. This variety gave significantly higher yield than all other varieties at 80 and 240 kg N/ ha. Perusal of data indicated that response of all the cultivars to fertilizer N reduced markedly as the dose of N rate increased.

However, the response to N application rate increased significantly in all varieties upto the highest levels of N (240 kg/ha), except in Kufri Sutlej, which responded only upto 160 kg N/ ha application.

Application of N at 240 kg/ ha increased tuber yield from 54 to 80% (Table 2) in different cultivars as compared to control. Maximum per cent increase in yield was recorded in Kufri Pushkar (79.7%) and Kufri Gaurav (78.6) %, whereas, minimum values were for Kufri Sutlej and Kufri Jyoti was 54%. Among the different nitrogen doses (80, 160 and 240 kg/ ha), maximum N response in terms of yield was observed at 80 kg/ ha(23 to 38%).

Table 2. Per cent yield response of nitrogen as affected by different potato cultivars.

Varieties

Yield response over control (%)

80 (kg N/ ha)

160 (kg N/ ha)

240 (kg N/ ha)

Kufri Jyoti

26.9

40.8

54.0

Kufri Jawahar

31.4

43.0

57.4

Kufri Bahar

27.9

42.9

60.9

Kufri Sutlej

22.8

43.9

54.0

Kufri Pukhraj

29.6

49.4

60.1

Kufri Pushkar

37.5

65.4

79.7

Kufri Gaurav

37.8

55.7

78.6

Kufri Surya

31.6

53.0

68.4

Potato cultivars differ in their growth and yield potential, hence there is a differential response to nitrogen and bulking rate even if they belong to same maturity group.

Number of tubers

Maximum number of total tubers was recorded in Kufri Pushkar followed by Kufri Gaurav and Kufri Jawahar at all levels of N (Table 3). The lowest number of tubers was observed in Kufri Pukhraj, followed by Kufri Bahar and Kufri Sutlej.

Table 3. Effect of different levels of nitrogen on total number of tubers (thousand/ ha).

Varieties

N levels (kg/ ha)

0

80

160

240

Mean

Kufri Jyoti

436

549

577

523

521

Kufri Jawahar

538

654

630

661

621

Kufri Bahar

413

501

437

457

452

Kufri Sutlej

400

474

511

518

476

Kufri Pukhraj

387

466

521

578

488

Kufri Pushkar

707

831

926

955

855

Kufri Gaurav

637

779

808

818

760

Kufri Surya

349

410

428

451

409

Mean

483

583

605

620

573

CD (0.05)

Varieties

37

N levels

26

VXN

73

In Kufri Jyoti, Kufri Jawahar and Kufri Bahar it was observed that as dose of nitrogen increased from 0 to 240 kg/ ha, the number of tuber decreased, which might due to utilization of applied N more towards tuber bulking rather than tuber numbers.

At initial dose of 80 kg/ ha higher number of potato tuber (20.4%) was observed in Kufri Pukhraj and similar trend was observed at higher dose of nitrogen application (240 kg/ ha) and it appeared to be a varietal character. In general, number of tubers followed the same trend as tuber yield.

Among all the cultivars under study maximum AUE was observed when minimum dose of N (80 kg/ ha) was applied. This was due to the fact that input-output relationship follows the law of diminishing return as far as the relationship between N and yield concerned. In general, increasing dose of N decreased the agronomic use efficiency among all eight cultivars.

The efficient cultivars gave higher tuber yield under nutrient stress (i.e. with less dose of N) than less efficient cultivars. The main reason of higher nitrogen efficiency in the presence of N was the capacity of a genotype to use/ absorb more N per unit from soil i.e. the ability of the root system of a genotype to acquire more N from soil.

Nitrogen requirement by different cultivars to obtain fixed yields

N rates for fixed yields obtained using quadratic equation showed that potato varieties differ greatly with regard to their nutrient use efficiency. The Kufri Gaurav required lower doses of nitrogen followed by Kufri Pushkar than other cultivars to produce particular fixed tuber yield (Table 5).

Net return increased with increase in N levels (Table 6). Kufri Gaurav gave maximum return at all N levels with mean net return of 107323/- followed by Kufri Pushkar ( 96382/-) and Kufri Pukhraj. The least net return was achieved on cultivation of Kufri Surya (mean 44326/-) followed by Kufri Jyoti ( 51022/-).

Kufri Gaurav and Kufri Pushkar proved to be the best variety as far as yield, AUE, targeted yield and net return are concerned. Total tuber yield of these two varieties obtained at 160 kg N/ ha could not be surpassed by any other varieties tested even with 240 kg N/ ha.

Similarly, the AUE of these two varieties at 240 kg N/ ha was significantly higher than all other varieties except Kufri Pukhraj at 0 and 80 kg N/ ha at all the levels of N. The amount of N required by Kufri Gaurav for providing 40 t/ ha yield was not sufficient for Kufri Jyoti, Kufri Badshah and Kufri Sutlej to produce even 30 t/ ha tuber. This variety gave the higher net returns, which were 11.4% higher than the second best cultivar Kufri Pushkar.

It can be concluded from the present study that yield and agronomic use efficiency can be improved markedly by exploiting varietal differences in potato. Potato cultivars showed wide variation in agronomic use efficiency (AUE) with respect to nitrogen.

Potato cultivar Kufri Gaurav was the highest yielder and agronomically most efficient variety followed by Kufri Pushkar and Kufri Pukhraj. This variety utilizes soil and applied N better than the other most common varieties of the region and convert, it into yield most economically.

Table 6. Net returns (Rs/ ha) different potato cultivars.

Cultivars

N (kg/ ha)

0

80

160

240

Mean

Kufri Jyoti

20846

37896

45701

51022

38866

Kufri Jawahar

24045

45294

51861

58510

44928

Kufri Bahar

23766

42357

51356

60634

44528

Kufri Sutlej

23687

38457

52016

55404

42391

Kufri Pukhraj

26856

47578

60774

65018

50057

Kufri Pushkar

35934

66156

88102

96382

71644

Kufri Gaurav

42582

75550

90133

107323

78897

Kufri Surya

10811

28015

39027

44326

30545

Conclusion:

Results revealed that Kufri Gaurav gave maximum yield and agronomic efficiency at all the levels of nitrogen followed by Kufri Pushkar and Kufri Pukhraj. Kufri Jawahar, Kufri Bahar and Kufri Sutlej were intermediate. Kufri Surya yielded minimum and gave least agronomic efficiency at all the levels of nitrogen.

Maximum number of tubers was produced in Kufri Pushkar followed by Kufri Gaurav. Whereas, Kufri Surya gave minimum number as compared to all the varieties. Kufri Gaurav proved to possess high tolerance to N stress and was the most nitrogen efficient variety followed by Kufri Pushkar and Kufri Pukhraj.

This variety required lower doses of N than other cultivars to produce a particular fixed yield in the same field. This variety can be useful for resource poor farmers as this produce higher yield compared to other released varieties even at lower doses of N.